Definition 1 of 2
To stir trouble
He needs one tight slap. How much gandmasti he is doing.
Added 2011-06-27 by mainmacha
Definition 2 of 2
Gandmasti means trouble or mischief of a sexual nature. It can refer to sleeping around, chasing women (not men), and being unfaithful.
That Raghupathy is up to gandmasti all the time. His wife will find out sooner or later.
Added 2011-07-27 by porkipaya